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5-27
5 Serial Gateway
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
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Sending Messages Using SendCmd Instructions in CPU Unit's User Program
The Unit converts the messages to Modbus-RTU protocol for in this operation.
Note 1 The header contains the following information.
• Remote destination network address (DNA): Network address to specify actual remote
Pocasset 0 (local network).
• Remote destination node address (DA1): Node address to specify actual remote Pocas-
set 0 (communications within local PLC).
• Remote unit address (DA2):
Unit address of serial communications port. An appropriate value is calculated and set
as follows:
When port 1 is used: Unit address = BYTE#16#80 + BYTE#16#04
×
Unit number (hexa-
decimal)
When port 2 is used: Unit address = BYTE#16#81 + BYTE#16#04
×
Unit number (hexa-
decimal)
2 The contents of the Modbus-RTU command enclosed in the message that is sent is as fol-
lows:
Slave address (binary) + FUNCTION code (binary) + Communications data (binary)
Start and CRC+End are not required when sending commands. They are added automati-
cally for serial communications.
System Configuration
CPU Bus-to-Serial Details
From the CPU Unit, it is possible to access OMRON
Inverters that are connected to the Serial Communi-
cations Unit via a serial network (Modbus-RTU).
2804
Serial Communications Unit
CPU Unit
Header
SendCmd
instruction
Message
RS-485 (Modbus-RTU)
Protocol
conversion
Modbus-RTU
command
Modbus-RTU
command
Modbus-RTU
Slave device (e.g,
OMRON Inverter)